Flooding Velocity Research Articles

Evaluation on the Dependence of Multiphase Flow and Reaction upon the Morphology of a Porous Media Network

A fixed-bed reactor or a catalyst particle can be considered as a porous media network, which is characterized by the pellet size, void fraction, and connectivity of the network. In a fixed-bed reactor, the percolation threshold was calculated to be 0.13−0.17, while the porosity of a fixed bed is ∼0.38; therefore, there is no percolation problem and a fixed bed can be modeled as a continuum medium. In multiphase flow, the connectivity of the network is much reduced due to the attachment of liquid film on the particles and an analogy was made between a trickle bed and a Bethe tree. It shows from this work that radial velocity profile estimation in a fixed bed could be obtained from transforming the bed space into a tube of a certain equivalent diameter, and the trickling to pulsing flow transition could be explained from its analogy to a Bethe tree. Electrical capacity tomography was employed to measure the dynamic liquid holdup in pulsing flow. Two types of packing have been identified from their different flooding behavior, and a quadralobe extrude was specifically designed to obtain the high flooding velocity. When the catalyst was internally wetted, the reaction rate was found to decrease linearly with the catalyst wetting fraction, nevertheless, and no percolation threshold was encountered, and this strange result was explained from the egg shell-type distribution of Pd beneath the support surface of only 0.4 mm.

Spacer Grid Effects during a Reflood in an Annulus Flow Channel

An experimental study has been performed to investigate the effects of a spacer grid in an annulus flow channel with a uniform power shaped single rod during a bottom-reflood phase. The ranges of the experimental parameters are 2-8 cm/s for the flooding velocity, 20-80°C for the inlet subcooling temperature, and 500-700°C for the initial wall temperature. Two types of spacer grids, i.e., a swirl-vane type grid and a straight egg-crate type spacer grid, have been tested to compare the differences in their thermal hydraulic behavior through the spacer grids. Flow patterns and a rewetting front behavior near a spacer grid are remarkably altered with the types of spacer grids used. In the case of a low flooding rate and a high wall temperature condition, the cooling capacity of the swirl-vane spacer grid is better than that of the straight egg-crate type grid. Rewetting velocities through the swirl-vane spacer grids are faster than those through the other types of grids. The cladding temperature of the heater rod near a spacer grid shows a different pattern with the types of spacer grid used.

Spacer Grid Effects during a Reflood in an Annulus Flow Channel

An experimental study has been performed to investigate the effects of a spacer grid in an annulus flow channel with a uniform power shaped single rod during a bottom-reflood phase. The ranges of the experimental parameters are 2-8 cm/s for the flooding velocity, 20-80°C for the inlet subcooling temperature, and 500-700°C for the initial wall temperature. Two types of spacer grids, i.e., a swirl-vane type grid and a straight egg-crate type spacer grid, have been tested to compare the differences in their thermal hydraulic behavior through the spacer grids. Flow patterns and a rewetting front behavior near a spacer grid are remarkably altered with the types of spacer grids used. In the case of a low flooding rate and a high wall temperature condition, the cooling capacity of the swirl-vane spacer grid is better than that of the straight egg-crate type grid. Rewetting velocities through the swirl-vane spacer grids are faster than those through the other types of grids. The cladding temperature of the heater rod near a spacer grid shows a different pattern with the types of spacer grid used.

Flooding velocity in long tubes

The primary results of measuring the flooding velocity in tubes 24, 28, and 50 mm in diameter in the air-water and air-dibutyl phthalate systems are presented. A partial empirical relation for the flooding velocity is proposed.

Counter-current gas–liquid flow in a vertical narrow channel—Liquid film characteristics and flooding phenomena

Results are reported of an experimental investigation of gas–liquid counter-current flow in a vertical rectangular channel with 10 mm gap, at rather short distances from liquid entry. Flooding experiments are carried out using air and various liquids (i.e., water, 1.5% and 2.5% aqueous butanol solutions) at liquid Reynolds numbers Re L < 350. Visual observations and fast recordings suggest that the onset of flooding at low Re L (<250) is associated with liquid entrainment from isolated waves, whereas “local bridging” is dominant at the higher Re L examined in this study. Significant reduction of flooding velocities is observed with decreasing interfacial tension, as expected. Instantaneous film thickness measurements show that under conditions approaching flooding, a sharp increase of the mean film thickness, of mean wave amplitude and of the corresponding RMS values takes place. Film thickness power spectra provide evidence that by increasing gas flow the wave structure is significantly affected; e.g., the dominant wave frequency is drastically reduced. These data are complemented by similar statistical information from instantaneous wall shear stress measurements made with an electrochemical technique. Power spectra of film thickness and of shear stress display similarities indicative of the strong effect of waves on wall stress; additional evidence of the drastic changes in the liquid flow field near the wall due to the imposed gas flow, even at conditions below flooding, is provided by the RMS values of the wall stress. A simple model is presented for predicting the mean film thickness and mean wall shear stress under counter-current gas–liquid flow, below critical flooding velocities.

Effects of Gas‐Agitation and Packing on Hydrodynamics and Mass Transfer of Extraction Column

AbstractThe effects of gas‐agitation and packing on hydrodynamics and mass transfer were investigated through experiments with air‐kerosene (benzoic acid)‐water system and corrugated‐packing of calendering plate with hole. The holdup of gas, holdup of dispersed liquid phase and mass transfer coefficient increase and the flooding velocity decrease with the increase in superficial gas velocity. Over‐agitation of gas causes over‐dispersion and emulsification of dispersed liquid phase, reduction of mass transfer performance and even flooding. The mass transfer performance of a packed column is far better than that of an unpacked column.

Theoretical and Experimental Investigation of the Flooding Velocity of an Immiscible Vapor Mixture Condensing in Vertical Tubes

A mathematical model accounting for the pressure oscillation when flooding occurs is presented to predict the velocity limit of an immiscible vapor mixture condensing in a vertical tube. This model incorporated the parameters of vapor inlet velocity, pressure drop, interfacial friction stress, tube inside diameter, and the fluid physical properties. The in-tube condensation experiments of an oil−steam vapor mixture with various mass ratios have been conducted using an 18 mm i.d. brass tube and a 20 mm i.d. glass tube, respectively. The model predicted that data agreed very well with the experimental data, indicating that this model is valid to predict the velocity limit of the immiscible vapor mixture condensing in a vertical tube.

The influence of small tube diameter on falling film and flooding phenomena

Flooding experiments have been carried out in vertical small i.d. tubes (6, 7, 8 and 9 mm), using smooth inlet and outlet conditions, with air and two liquids (water and kerosene). Experimental data on free falling film characteristics have also been obtained, in the same test sections, which aid the interpretation of flooding phenomena. These new data suggest that the tube diameter strongly affects film flow development, possibly promoting wave interaction and damping. In turn, the wavy film evolution essentially determines flooding characteristics. At small liquid Reynolds numbers ( Re L<300) critical flooding velocities, U G, follow a trend already reported in the literature, i.e. decreasing with increasing liquid rate. However, at higher Re L the trend is reversed, i.e. increasing U G with increasing liquid rate. This has not been reported in the literature before and may be attributed to damping of waves. At still higher Re L, another region is evident in the flooding curves, characterized by nearly constant flooding velocity. The dominant mechanism in almost all cases is wave growth and upward dragging by the gas, initiated at the liquid exit.

Critical Heat Flux of Counter-Current Two-Phase Flow in Vertical-Narrow-Annular Flow Passages.

The critical heat flux of the counter-current flow in narrow-annular flow passages (δ=0.5∼10.0 mm) was examined by using R-113 vapor and liquid at 0.1 MPa for the bottom closed and the open system. When the clearance δ≤2.0 mm, the falling liquid flow rate was restricted by the upward vapor flow in the bottom open system, which was expressed with the Wallis type flooding correlation. The heat flux at the initiation of the temperature excursion (EXC) was well predicted for both the bottom closed and the open system by considering that the EXC occurs when the falling flow rate becomes equal to the evaporation rate under the liquid falling limiting. In the case of δ=5.0 mm, the liquid penetration was also restricted, however it was much lower than the Wallis flooding velocity. It was rather predicted with the flooding by the level swell of the two-phase mixture with the falling film. After the penetration limiting, the falling flow rate became equal to the evaporation rate, and then the EXC was initiated after a further increase in the heat flux. In the case of δ= 10.0 mm, the EXC started like the pool boiling without any penetration limiting. The EXC heat flux correlation for δ=2.0∼10.0 mm was derived by considering that the EXC occurs when the mixture void fraction exceeds a critical value.

Froth Heights on Dual-Flow Trays with a Heterogeneous Binary Azeotropic System and a Heterogeneous Ternary System with a Homogeneous Azeotrope

Visual froth height measurements and the clear liquid heights on 20% free area dual-flow trays, operated at total reflux, have been obtained on the homogeneous system of water−steam, on the heterogeneous systems of ethyl acetate−water and ethyl acetate−ethanol−water, and in the homogeneous region near the homogeneous ternary azeotrope of that ternary system. The experimental results were obtained under distilling conditions at a total pressure of 101.3 kPa for a range of liquid and vapor densities and vapor velocities. The churn flow conditions on the dual-flow trays at total reflux were found to have the characteristic of constant volume fraction liquid in the froth for all systems investigated: ΦL = 0.291; hf < 0.300. A correlating equation for the froth height that contains the impact pressure was found for all systems investigated to be hf = 2.625(1/2ρVu2) with hf < 0.300. A dimensionless correlating form, based on a modified Froude number, was found to be suitable for all systems: FrM = 280.0 × 10-6(ρV/ρL)-1/2 with hf < 0.300. The clear liquid height was found for all systems to follow hCL = ΦLhf with hf < 0.300. The dimensionless correlation for froth heights for all systems could be converted to a flooding vapor velocity relationship at total reflux for dual-flow trays by ufl = 0.0283√Z(ρV/ρL)-3/4 with Z < 0.300.

Visual observations of flooding in narrow rectangular channels

New flooding data in a vertical rectangular channel with 5 and 10 mm gap between its main parallel plates are reported. Visual observations and fast recordings are made to determine conditions associated with the onset of flooding in the channel. For the 10 mm gap channel a combination of mechanisms, i.e., levitation and upward transportation of laterally coherent or isolated waves, and local wave bridging, appear to be responsible for triggering flooding. The critical flooding velocity is curiously nearly independent of liquid flow rate above film Reynolds number approximately 500. In the 5 mm gap channel and for small Re L, flooding occurs at the liquid entrance, whereas “massive” wave bridging, occurring above the middle of the test section, is the dominant flooding mechanism for relatively higher Re L. Predictions based on small amplitude stability analysis are in good agreement with flooding data from the latter case.

Performance of wire mesh mist eliminator

An experimental study was made to measure the performance of wire mesh mist eliminator as a function of broad ranges of operating and design conditions. The experiments were carried out in an industrial scale layered type demister pad made of 316 L stainless steel wires. The demister performance was evaluated by droplet separation efficiency, vapor pressure drop of wet demister, and flooding and loading velocities. These variables were measured as a function of vapor velocity (0.98–7.5 m/s), packing density (80.317–208.16 kg/m 3), pad thickness (100–200 cm), wire diameter (0.2–0.32 mm), and diameter of captured droplets (1–5 mm). All the measurement results lie in ranges where, in practice, the wire mesh mist eliminator predominates. The experimental results indicate that the separation efficiency increases with both the maximum diameter of capture water droplets and the vapor velocity and with the decrease of wire diameter. The pressure drop for the dry demister is relatively low and depends only on the vapor velocity. The pressure drop increases linearly up to the loading point, thereafter; the rate of increase is larger. Beyond the flooding point, the increase rate is significant even for the slightest rise in the vapor velocity. The flooding velocity diminishes with the beef-up of the packing density and with the decrease of the wire diameter. Three empirical correlations were developed as a function of the design and operating parameters for the separation efficiency, pressure drop for the wet demister in the loading range, and the flooding and loading velocities. These correlations are sufficiently accurate for practical calculations and demister design. The temperature depression corresponding to the pressure drop in a wire mesh mist eliminator systems installed in a typical multi stage flash desalination plant was estimated from the developed correlation. A good agreement was obtained between the design values and the correlation predictions.

Level Swell and Flooding of R113 Two-Phase Mixture with a Falling Film in Vertical Pipes.

Using R 113 vapor and liquid, behavior of the two-phase mixture level was examined in both cases of bubbling a stagnant liquid column in vertical pipes and bubbling a liquid column to which liquid was supplied as a falling film. The pipe diameters used were 10.0, 14.8, 20.2 and 26.0 mm. The initiation condition of flooding in the latter case was also examined. Observed phenomena were quite similar to those in previous air-water experiments. However, the level fluctuation amplitude and the mixture level swell height in the experiments with the falling film were smaller than those in the air-water experiments. Physical models devised to predict the mixture level height and the flooding velocity under a slug flow condition, which were developed in previous work, were found to reproduce the experimental results well.

Initiation conditions of liquid ascent of the countercurrent two-phase flow in vertical pipes (in the presence of two-phase mixture in the lower portion)

Experiments on the countercurrent two-phase flow of air and water were conducted using vertical pipes of 10–26 mm in diameter to investigate the initiation conditions of liquid ascent. When a liquid film flowed down to a bubbling two-phase mixture in the lower portion of the pipe, liquid ascent began at much lower gas velocities than usual flooding velocities without the bubbling two-phase mixture. In most cases, liquid ascent occurred in a slug flow state. The initiation conditions of the liquid ascent were analyzed physically by considering the level swell of the two-phase mixture fluctuating around the mean height.

Flooding of Counter-Current Two-Phase Flow of Gas and Liquid. 1st Report. On Flooding in Vertical Circular and Annular Channel.

Experinlental investigations arc performed on flooding which occurs in vertical circular and annular channels. Water film flows down along the channel surface through porous cylinders, and air is raised from the channel bottom by a suction pump. The ooding velocity of the circular tube is proportional to the diameter ill agreement with earlier investigations For the annular channel, a ratio of liquid flow rates of both channel surfaces has a strong effect on the flooding velocity. The conventional method cannot predict the flooding velocity. In the present study, a characteristic diameter of the annular channel is determined by the ratio of liquid flow rates for Reynolds number of liquid and gas. The flooding velocity is approximately indicated as a uniform curvature with the Reynolds number of liquid.

Characteristics of the Onset of Flooding for Countercurrent Air-Water Flow in Vertical Annuli with a Direct Injection Mode

An experimental work was conducted to investigate the characteristics of the onset of flooding in vertical annuli with a direct injection mode using air and water. The onset of flooding was determined by means of pressure drop measurement while the air velocity was increased gradually under fixed liquid flow rates. Data of the onset of flooding were collected for various combinations of the tube size and the nozzle number. A theoretical analysis of the onset of flooding was also performed based on an envelope theory. The result shows that the onset of flooding in small-scale annuli can be predicted relatively well by the theory. A modified Wallis parameter was used to investigate the scaling effect of flooding phenomena in the annuli, indicating a relatively reasonable result. The number of nozzle has no effect on the flooding velocity when liquid was injected through 2, 3, 4 and 6 nozzles but the initiation of flooding was significantly expedited when 12 nozzles were employed for liquid injection.

Initiation Conditions of Liquid Ascent of the Countercurrent Two-phase Flow in Vertical Pipes. In the Presence of Two-Phase Mixture in the Lower Portion.

Experiments on the countercurrent two-phase flow of air and water were conducted using vertical pipes of 10 to 26mm in diameter, to investigate the initiation conditions of liquid ascent. When the liquid film flowed down to the bubbling two-phase mixture in the lower portion in the pipe, liquid ascent began at much lower gas velocities than usual flooding velocities without the bubbling two-phase mixture. In most cases, liquid ascent occurred in a slug flow state. The initiation conditions of liquid ascent were analyzed physically by considering two-phase mixture level swell fluctuating around the mean height.

Flooding in inclined pipes with obstructions

The flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a tube in which a gas is flowing upwards. As is known, the entrainment effect can completely prevent the liquid fall from achieving its natural flow. Tube inclination angle has a dramatic effect on flooding velocity. The present work deals with air-water experiments carried out with a transparent circular duct test section with the aim of evaluating the influence of slight deviations from the vertical position on flooding parameters in the presence of obstructions in the channel. An improvement of the Taitel et al model for the prediction of the onset of flooding in inclined pipes is proposed.

溶液の粘弾性を考慮したポリマー攻法の解析 その２．一次元ポリマー攻法の室内実験

To study how the viscoelastic flow behavior of polymer solution described in Part. 1 (ref. 1) had an effect on oil-recovery performance, 1 D flood experiments were carried out with glass-bead packed cores. Two white mineral oils of viscosity about 25mPa•s and 50mPa•s were used as displaced fluids. In each experiment, water and polymer floods were done with the same core at a relatively-high flooding velocity above 16μm/s. In polymer floods, polymer concentration of effluents was measured by the spectrophotometric method of M.W. SCOGGINS and J.W. MILLER.In polymer floods, oil was recovered faster as flooding velocity became faster. In high flooding velocity, interstitial velocity of polymer solution in the core becomes high and shear rate for flow becomes larger, too. The viscoelastic flow behavior of polymer solution that increased its viscosity with increasing shear rate was thought to improve mobility ratio and make oil recovery faster. By analysis of polymer-concentration histories of effluents, water bank was observed to be produced from the core before breakthrough of injected polymer solution. This water bank was thought to originate from mobile water which was initially present in the core before the flood. The histories of pressure of oil and water phase at the center of cores during flood experiments were measured separately with semi-permeable filters made of teflon and ceramics. Oil pressure could be measured well, but the method to measure water pressure was remained to be a problem.These data obtained in this study will be compared with calculated results by the simulater in the next paper.

Adjustment Factors for Flood Damage Curves

Estimates are provided for quantifying adjustments to depth–damage tables as a result of flooding events of different types on residential dwellings. The adjustments reflect estimated changes to flood damages due to the availability of flood warning, long durations of flooding, and ice and high velocity flow. Regression analyses are described that examine the degree to which a range of variables, including a resident’s experience with flooding, householder income, floor area of residence, and assessed value of property, can explain the variability of flood damage curves.